Apparatus for continuously producing raw juice by diffusion, especially for the production of sugar

ABSTRACT

A raw juice producing apparatus originally designed for the leaching of sugar cane raw material is adapted for use with sugar cane raw material and/or with sugar beet raw material. For this purpose a substantially horizontally travelling conveyor, the upper run of which travels over a sieve or screen bottom in a trough, is provided with an endless cover made of a fabric or netting that is permeable to liquid. Preferably, the total length of the cover comprises a plurality of fabric or netting sections secured to carrier members of the travelling conveyor. Cleaning means are arranged for cooperation with the lower run of the conveyor for maintaining the liquid permeability of the fabric or netting.

United States Patent 1 [111 3,731,613 Wolff et al. 1 May 8, 1973 [541APPARATUS FOR CONTINUOUSLY 2,686,192 8/1954 Bonotto ..99 27s PRODUCINGRAW JUICE BY 3,380,373 4/1968 Lenz DIFFUSION, ESPECIALLY FOR THE3,436,226 4/ 1969 Schaus ..99/278 PRODUCTION OF SUGAR Inventors:Reinhard Wolff; Walter Qietzel,

both of 3300 Braunschweig, Germany BraunschweigischeMaschinenbauanstalt, Braunschweig Am Altem Bahmohof, Germany Filed: Jan.19, 1972 Appl. No.2 219,067

Assignee:

6/1925 Wittig ..l98/230 Primary Examiner-Robert W. JenkinsAttorney-Wolfgang G. Fasse [57] ABSTRACT A raw juice producing apparatusoriginally designed for the leaching of sugar cane raw material isadapted for use with sugar cane raw material and/or with sugar beet rawmaterial. For this purpose a substantially horizontally travellingconveyor, the upper run of which travels over a sieve or screen bottomin a trough, is provided with an endless cover made of a fabric ornetting that is permeable to liquid. Preferably, the total length of thecover comprises a plurality of fabric or netting sections secured tocarrier members of the travelling conveyor. Cleaning means are arrangedfor cooperation with the lower run of the conveyor for maintaining theliquid permeability of the fabric or netting.

10 Claims, 3 Drawing Figures APPARATUS FOR CONTINUOUSLY PRODUCING RAWJUICE BY DIFFUSION, ESPECIALLY FOR THE PRODUCTION OF SUGAR BACKGROUND OFTHE INVENTION The invention relates to an apparatus for the continuousextraction of raw juice by diffusion. More specifically, such apparatusmay comprise a long covered trough with an inner screen or sieve bottom.The raw material is transported through the trough by means of severalparallel conveyors including chains connected in pairs by carriermembers and driven by drive means so that the upper runs of theconveyors travel above the screen bottom for transporting the preparedraw material to be leached for said raw juice extraction in alongitudinal direction. The lower run or runs of these conveyors traveloutside the trough.

Those skilled in the art of sugar manufacture have been trying for along time now to find means for using the machinery and equipment of asugar factory optionally either for the processing of sugar cane or ofsugar beets. The solution of this old problem would result in aconsiderable increase in the productivity of sugar factories, especiallythose which due to their location permit an economic delivery of sugarbeets and sugar cane. Assuming that the harvesting of sugar beets wouldnot coincide with the harvesting of sugar cane, it would be possible tooperate the respective sugar factory throughout the year or at leastconsiderably longer than it is presently the case having regard to therelatively short harvesting periods.

For instance, it is common in the cane sugar industry to willinglyaccept losses by starting the harvest before the cane has the degree ofripeness which guarantees maximum sugar yield. Moreover, the harvestingtime is extended beyond the optimum ripeness which again results insugar losses. However, a maximum harvesting period of6 months only canbe achieved in such a way.

The harvesting of sugar beets cannot be extended to such length sincethe harvest must generally be completed before frost sets in. Theincreasing mechanization in harvesting beet crops has not onlyrationalized the harvesting itself but has also considerably expeditedit. Thus, the producer can generally deliver the beets to the sugarfactories within a few weeks. The sugar factories are able to receiveand store large quantities of beets, but, for the same reasons as areprevailing in connection with the processing of sugar cane, they cannotstore the beets over randomly prolonged periods of time since storedsugar beet respirate sugar and, thus cause a sugar loss.

The sugar production from sugar beets and the sugar production fromsugar cane differ from each other only with respect to the raw juiceextraction or production. Therefore, a device which may be usedoptionally for the raw juice extraction from prepared sugar beets orfrom prepared sugar cane, would represent a great advantage in theplanning of sugar factories as it would be possible to largelystandardize such factories.

Up to now, a satisfactory solution of this problem of using the sameapparatus for different raw materials has not yet been found, presumablybecause raw juice from sugar cane has been extracted by mechanicalpressing of the cane in three-roller mills whereas raw juice from sugarbeets or beet cossettes has been produced by a diffusion processpreferably effected in a diffusion tower. The special advantage of thisdiffusion process was the possibility of effecting the leachingcontinuously and the highly efficient yield of highquality raw juice.However, the diffusion towers in which sugar beet cossettes are leachedcannot be used for the processing of sugar cane because sugar canecannot be brought into a similar condition as beet cossettes withrespect to transporting the raw material through the diffusion tower.Broken and crushed sugar cane rather tends to form lumps and plugs whichblock the conveying flights or wings inside the tower.

It is quite conceivable to feed crushed or shredded sugar beets throughthree-roller mills being the device for the raw juice extraction fromsugar cane in a sugar factory. However, the result would be sugar beetpulp, that is, the beets or the beet cossettes are merely comminutedfurther by the three-roller mills without extraction of any raw juice asis the case with sugar cane. Raw juice extraction would then have to beeffected by hydraulic presses or other devices which have not been usedfor a long time now due to their well known disadvantages relating, forinstance, to juice quality. Consequently, it will be appreciated thatthe technologies of raw juice extraction from cane and beets differ fromeach other to a considerable extent.

The above mentioned device for the continuous raw juice extraction bydiffusion which comprises a horizontal conveyor is intended for theprocessing of sugar cane. The development of such a device means thatthe raw juice extraction by diffusion which has been applied with highyield to sugar beets can now also be applied for the processing of sugarcane. Thus, both technologies have become somewhat similar as in bothinstances diffusion or leaching is employed.

However, the practice has shown that the known device mentioned at thebeginning is not suitable for the processing of beet cossettes becausethe beet cossettes which are transported in a layer over the screenbottom are ground or comminuted to an undesirable extent by the shearingforces arising at the contact sur face at the screen bottom. The resultis a relatively high percentage of sugar beet pulp from which raw juicecan be extracted if ever by means of presses, but not in an economic wayby diffusion. Moreover, the beet pulp would clog the screen openings inthe screen bottom so that the juice circulation which is indispensablefor the leaching of sugar beet cossettes, is cut off.

OBJECTS OF THE INVENTION ln view of the foregoing, the invention aims atachieving the following objects singly or in combination:

to provide an apparatus which may be used with equal efficiency for theproduction of raw juice regardless whether beets or cane are used as thestarting material; to avoid the above outlined drawbacks of the priorart devices while simultaneously combining the advantages in a singleapparatus; to adapt the apparatus generally employed for the productionof raw juice from sugar cane also for the production of raw juice frombeet cossettes by difi'usion; to avoid that the sugar beet cossettes arecomminuted to an undesirable degree during the diffusion process;

to assure an equally high purity of the resulting raw juice regardlesswhether beet cossettes or prepared sugar cane are used as a startingmaterial in the same apparatus; and

to arrange the conveyor means in the above mentioned apparatus in such amanner that maintenance and repair as well as cleaning are facilitated.

SUMMARY OF THE INVENTION According to the invention the above objectshave been achieved in an apparatus which comprises substantiallyhorizontally travelling conveyor means for transporting the shredded orcrushed starting material through a diffusion trough having a screenbottom whereby the upper run of the conveyor means travels through thetrough above said screen bottom and the lower run returns outside thetrough, wherein the conveyor means comprise power driven endless chainsand carriers connecting each pairs of said chains and arranged in spacedrelation to each other and a belt made of fabric or netting and isarranged to extend between the screen bottom of the trough and thematerial to be leached. The fabric or netting is permeable to liquid andconnected to the conveyor carriers. Cleaning means are provided over thelength of the bottom run of the conveyor means in order to maintain theliquid permeability of the netting or fabric.

The invention prevents a contact between the layer of the beet cossettesto be leached and the screen bottom due to the permeable netting whichis supported by the conveyor means such as carrier members.Consequently, the beet cossettes lying in the lower layer or zone remainmechanically unaffected and keep their structure or shape necessary fora satisfactory leaching during their travel through the trough. Since nobeet cossettes are further comminuted, there will also be no beet pulpwhich could clog the screen openings of the screen bottom and interruptthe juice flow. Therefore, it is now possible to continuously produceraw juice of high quality and high yield from beet cossettes by means ofthe device according to the invention.

Another advantage of the apparatus according to the invention is seen inthat it can also be used for the processing of sugar cane without anymodification. However, it is also very simple to remove the fabric beltor netting from the carriers of the conveyor chains in case sugar caneis to be processed and to replace it in case beet cossettes are to beprocessed.

The cleaning means for the netting is located outside the trough in theregion of the bottom run of the conveyor and prevents the formation ofinfection points and to maintain permeability of the netting. Thus,slimy substances which arise unavoidably during the processing of beetcossettes are prevented from clogging the netting pores.

BRIEF FIGURE DESCRIPTION In order that the invention may be clearlyunderstood, it will now be described, by way of example, with referenceto the accompanying drawings, wherein:

FIG. 1 shows a schematic side view of the essential elements of a devicefor the continuous raw juice exv traction by diffusion;

FIG. 2 shows a sectional view of the device of FIG. I on an enlargedscale illustrating the structure of the present conveyor; and

FIG. 3 shows a sectional view along line III-Ill in FIG. 2.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS FIG. 1 illustrates a partialview of a diffuser apparatus or device for the continuous raw juiceextraction by diffusion. This diffuser is constructed according to theknown so called Egyptian system and is only suitable for the continuousleaching of sugar cane unless it is modified as taught by the presentinvention.

The shown device 1 or diffuser comprises a long trough 2 which issubstantially flat and covered at the top. The trough is equipped withan inner screen bottom 3. The material 14 (FIG. 2) to be leached istransported into the trough by an infeed conveyor 4 and then slowlydragged through the trough 2 over the screen bottom 3 by means of aconveyor 4 comprising several parallel conveyor chains arranged over thelength of trough 2. The chains slide above the screen bottom 3 and areconnected in pairs by carrier members extending across the conveyingdirection which is from left to right in FIG. 1.

The conveyor chains 4 travel with their upper runs 5 on the screenbottom while the lower runs 6 are located below the trough 2. At the endof the trough 2 the layer of the leached material 14, bagasse in case ofsugar cane is being processed, is dewatered or pre-dewatered,respectively, and then discharged. I

The leaching of the material 14 is started before entering the trough byadding juice of appropriate, high temperature through feed pipe 7a towhich the juice is supplied by heat exchangers not shown, to the rawmaterial on the infeed carrier 4' so that for instance, beet cossettesare heated to temperatures of approximately to C. Thejuice runningthrough this fresh material, such as cossettes, is drawn off below theinfeed carrier 4' and conveyed through discharge pipes 8 as feed juicefor further processing.

The leaching of the material 14 in the trough 2 is further effected byadding circulation juice of a certain temperature through feed pipes 7to the material entering at the inlet side. In the region below thesefeed pipes there are discharge pipes 8a through which the juice leavesafter percolating through the material layer 14. This juice is fed tothe heat exchanger and then through the feed pipe 7a to the startingmaterial.

Further discharge pipes 9 are located under the trough 2 along itslength for discharging the leaching liquid and again adding it to thematerial by pumps 10 through feed pipes l 1 arranged at a certain pointahead of the discharge point as seen in the transporting direction ofthe material to be leached. In this way, the leaching liquid travelsthrough the trough 2 from the outlet side of the trough toward its inletend and thus opposite to the transporting direction of the material tobe leached because the juice is continuously discharged and readded.Fresh water is added through feed pipe 12 and recovered liquid or socalled press water may be added through further feed pipe 13 as desired.A leaching process is effected in this way which is almost identical tothe countercurrent principle applied in diffusion towers for theprocessing of sugar beet cossettes.

The special advantage of this countercurrent principle is that asubstantially constant concentration gradient is obtained between theliquid and the material to be leached over the entire duration of theleaching process. The sugar content of the material to be leached has,for instance, become very low at the outlet end of the trough 2. Thefresh water added at this point through feed pipe 12, however, does notcontain any sugar so that the concentration gradient necessary forefficient leaching is obtained. The concentration of liquid increaseswith an increasing number of flows of leaching liquid through thematerial, the liquid, on the other hand, is added to the material ofrising sugar concentration toward the infeed end of the trough 2 so thatthe concentration gradient indispensable for efficient leaching isassured in a continuous manner and a high efficiency can thus beobtained.

This type of leaching by percolating liquid has a further advantage withrespect to the quality of the produced raw juice since the layer of thematerial 14 in trough 2 acts as a filter for solid impurities, so thatthe discharged feedjuice is ofa surprisingly high purity.

FIG. 1 does not show the equipment for the preparation of the materialto be leached. However, such equipment is not part of the invention andcan precede trough 2 depending on the kind of material. Crushingmachines and comminuting apparatus will be used for the preparation ofsugar cane, beet crushing machines, especially slicers, are necessaryfor the production of beet cossettes.

The leached material in case of sugar cane it is bagasse which ispre-dewatered at the end of trough 2 is further processed by respectiveequipment depending on its nature. The units necessary for this purposeare known and can be readily used.

The diffuser so far described has been developed for the leaching ofsugar cane and is not suitable for the extraction of raw juice fromsugar beet cossettes. FIGS. 2 and 3 show the essential features of theinvention for modifying the apparatus to use it optionally for sugarcane diffusion and/or for the leaching of sugar beet cossettes. FIG. 2shows a longitudinal section through a portion of the screen bottom 3 ofthe trough 2. This longitudinal section also shows part of the conveyorchain 4, particularly its upper run 5. Above the upper run 5 there isshown the layer of the material 14 to be leached. The conveyor chain 4is preferably a sprocket chain, the links of which comprise pairs ofinside links 15 and pairs of outside links 16 which alternate with eachother. Carrier members 17 are attached at certain intervals to theinside links 15. These carrier members extend transversely to thedirection of travel. Preferably, these carrier members 17 have the formof flat bars in a diffuser for the leaching of sugar cane.

In order to avoid the detrimental contact between the layer 14 of sugarbeet cossettes and the screen bottom 3, for reasons as explained above,the invention provides a belt of fabric or netting 18, for instance afilter netting, which is permeable by the liquid or juice and the upperrun of which carried by the carrier member travels between the layer 14and the screen bottom 3. Such netting 18 is located on the top side ofthe carrier members 17. This filter netting l8 separates the layer ofsugar beet cossettes 14 from the surface of screen bottom 3 and, thus,safely avoids that shearing forces have an effect on the lower sugarbeet cossette layers and that the latter are crushed to pulp.

The belt netting or fabric may be endless or, as in the illustratedembodiment, the liquid permeable netting may be subdivided into surfaceelements 19. As seen in the length of the conveyor chains 4, thesesurface elements 19 of the netting 18 should have such a size that theyat least span the distance between two successive carrier members 17. Acertain additional length is provided in order to attach the surfaceelements 19 at the front and rear edge.

The width of these surface elements 19 extends laterally close to theoutside links 16 of the conveyor chains 4. In this way, the surface ofthe screen bottom 3 located between each of two conveyor chains 4forming a pair is covered by netting, and a belt of liquid permeablenetting 18 comprising the surface elements 19 is formed which endlesslyextends over the total length of the endless conveyor chains 4.

Depending on the properties of the netting 18, it may be advantageousthat the length of the surface elements 19 is such that one elementspans at least the distance between three successive carrier members 17.FIG. 2 shows, especially how the front and rear edges 20 and 21 ofsurface elements 19 are attached to modified carrier means 22 whichdiffer from carrier means 17 in that they particularly for this purpose,are constructed as two piece members. As can be seen from FIG. 2 themodified carrier means has round edges to assure a gentle fit of thenetting 18. The ends of the surface elements 19 are attached by suitableclamping ledges 23 to the bottom side of both members of the furthercarrier means 22. Turnbuckles may also be used to stretch and attach thesurface areas 19. Attentionis to be paid that there is no gap betweenboth members of the further carrier means 22 after assembly.

The lateral edges 24 of the surface elements 19 are constructed ashemstitches 25 into which is inserted a strand type support 26 which issecured to the carrier means 22 in any suitable manner. This strand typesupport 26 can, for instance, be a metal or plastic rope whichstrengthens the lateral edge 24 of the surface elements 19 so that itdoes not yield under the load of the material 14 whereby beet cossettesare prevented from entering into the region between the screen bottom 3and the netting 18. It is also advantageous to support the width of thesurface elements 19 by additional strand type supporting elements 26a asshown in FIG.

Since the conveyor chains 4 comprise inside and outside links 15 and 16,a gap results between the lateral edge 24 of every surface element 19and the adjacent inside link 15 through which sugar beet cosettes couldpass. Therefore, covering elements 27 of preferably roof-shaped crosssection which also cover the conveyor chains 4 are arranged along everylateral edge of the surface elements 19. These covering elements 27reach with their bottom edges as close as possible to the top surface ofthe elements 19 without endangering the surface elements 19 of thenetting 18. The covering elements (not shown) at the lateral walls ofthe trough 2 or rather at both outside conveyor chains 4 need not beroof-shaped but may be simply inclined surfaces. Thus, beet cossettesare largely prevented from entering the region between the screen bottom3 and the netting 18.

The netting l8 prevents a contact of the material 14 to be leached withthe screen bottom 3. Consequently,

shearing forces between the material and the screen bottom are missingwhich would otherwise provide a cleaning action along the screen bottom3. In order to avoid possible deposits which could clog the screenbottom and also to prevent the formation of infection spots, at leastone carrier member 17 of every pair of conveyor chains 4 is equippedwith a cleaning device 28. A simple embodiment of such a cleaning devicemay comprise a rubbing bar 29, made of a soft or rubber-elastic materialfor producing shearing forces between such bar and the surface of thescreen bottom 3 when the bar is dragged over the screen bottom.

In order to keep the filter netting 18 clean, a cleaning device 30 islocated in the region of the lower run 6 and equipped with high-pressurenozzles 31 which spray the netting 18 as it passes these nozzles.

The above described embodiment of the invention comprising the nettingsurface elements 19 with reinforced lateral edges and with front andrear edges secured to the carrier means 22 has the advantage that thesmall netting elements for instance a filter netting are relatively easyto handle and to attach to the chains without any undesired effects dueto elongation or other changes in size which may occur during operation.Another advantage is seen in that such smaller surface elements can beeasily exchanged and it is not necessary to exchange the completenetting surface over the total length of the conveyor chains but merelythe elements which may have been worn out. The hemstitch construction ofthe edges and the reinforcing of the lateral edges of the nettingassures a low wear and tear of the fabric or netting by the stresscaused by the material 14 to be leached. Moreover, such edgeconstruction provides an efficient counter action against the tendencyof the material to enter into the region between the lateral edges ofthe surface elements or netting and the conveyor chain running directlynext to it. It has been found that a quite efficient size for thesurface areas 19 is obtained if these areas extend over at least threesuccessive carrier members.

The most suitable conveyor means for the present purposes are sprocketchains although an open slot results between the lateral edge of thenetting and the inside link 15 as mentioned above. This gap causes noproblems since it may be easily covered as described above. Besides, anydeposits which may be formed on the screen bottom 3, especially in theproduction of juice from sugar beet cossettes, in-spite of the edgecovers, may be removed by said cleaning device 28, attached to at leastone carrier member 17 of every conveyor chain pair. i

Furthermore, it is important for the satisfactory leaching of sugar beetcossettes that the recirculation of the liquid is effected in apredetermined pattern so that the liquid percolating through thematerial 14 to be leached from the top to the bottom may not turn asidein a horizontal component and does not become mixed with juice of adifferent concentration. Therefore, the apparatus according to theinvention is equipped with suspended drag sheets 32 in the region of theliquid feeding points along the top portion of the trough 2 as shown inFIG. 1. These drag sheets guide the liquid in the desired direction andalso avoid the formation of foam. This is an advantage because theformation of foam would, otherwise, affect the further processing of thejuice or rather its flow and removal as well as the circulation pumping.

Although the invention has been described with reference to specificexample embodiments, it is to be understood that it is intended to coverall modifications and equivalents within the scope of the appendedclaims.

What is claimed is:

1. In an apparatus for the continuous raw juice production by diffusionwherein a long, covered trough is provided with a screen bottom, whereinraw material conveyor means travel with their upper run through saidtrough above the screen bottom for transporting prepared raw materiallongitudinally through the trough, and wherein the conveyor means returnwith their lower run outside said trough, the improvement comprisingliquid permeable netting means forming a belt as a cover of saidconveyor means, carrier members of the conveyor means for supportingsaid belt and for connecting the belt to said conveyor means andcleaning means arranged for cooperation with said lower run of said beltwhereby said belt is maintained liquid permeable.

2. The apparatus according to claim 1, wherein said netting meansforming the belt comprise a plurality of surface elements having frontand rear edges as viewed in the conveying direction, clamping means forsecuring said front and rear edges to the carrier members of theconveyor means, said surface elements further comprising lateral edgesforming longitudinal tubular means, and strand type supporting meansextending longitudinally through said tubular means in the conveyingdirection.

3. The apparatus according to claim 2, wherein said longitudinal tubularmeans are formed by a hemstitch.

4. The apparatus according to claim 2, wherein said conveyor meanscomprise pairs of conveyor chains connected by that said carriermembers, and wherein the surface elements of netting have a lengthextending over at least three successive carrier members as viewed inthe conveying direction, said lateral edges of the surface elementsextending close to said conveyor chains.

5. The apparatus according to claim 4, wherein said conveyor chains aresprocket chains, said apparatus further comprising covering means forcovering said lateral edges of the surface elements of netting towardthe raw material, whereby the covering means prevent the raw materialfrom entering into the space between said screen bottom and said upperrun.

6. The apparatus according to claim 2, comprising further strand typesupporting means arranged longitudinally below said netting meanssurface elements and intermediate said lateral edges of said surfaceelements.

7. The apparatus according to claim 1, comprising further cleaning meansattached to at least one of said carrier members for cleaning saidscreen bottom.

8. The apparatus according to claim 7, wherein said further cleaningmeans comprise a bar of yieldable material having a surface positionedin contact with the screen bottom whereby cleaning shearing forces areproduced when the conveyor means move.

9. The apparatus according to claim 1, wherein said first mentionedcleaning means for the netting means is equipped with high pressurenozzles.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION patent 3,751 ,613Dat d May 8, 1973 Reinhard Wolff et a1 Inventor(s) It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

On the cover sheet [73] Am Altem Bahmohof, Germany" should read Am,Alten Bahnhof, Germany insert [30] Foreign Application Priority DataGermany 2 103 164.1 Jan. 23,1971

Signed and sealed this 15th day of October 1974.

(SEAL) Attest:

MCCOY M. GIBSON JR. I C. MARSHALL DANN Attesting, Officer Commissionerof Patents USCOMM-DC 60376-P69 us coVERu-MEM PRINTING orncs: 93 0 FORMPO-105O (10-69)

1. In an apparatus for the continuous raw juice production by diffusion wherein a long, covered trough is provided with a screen bottom, wherein raw material conveyor means travel with their upper run through said trough above the screen bottom for transporting prepared raw material longitudinally through the trough, and wherein the conveyor means return with their lower run outside said trough, the improvement comprising liquid permeable netting means forming a belt as a cover of said conveyor means, carrier members of the conveyor means for supporting said belt and for connecting the belt to said conveyor means and cleaning means arranged for cooperation with said lower run of said belt whereby said belt is maintained liquid permeable.
 2. The apparatus according to claim 1, wherein said netting means forming the belt comprise a plurality of surface elements having front and rear edges as viewed in the conveying direction, clamping means for securing said front and rear edges to the carrier members of the conveyor means, said surface elements further comprising lateral edges forming longitudinal tubular means, and strand type supporting means extending longitudinally through said tubular means in the conveying direction.
 3. The apparatus according to claim 2, wherein said longitudinal tubular means are formed by a hemstitch.
 4. The apparatus according to claim 2, wherein said conveyor means comprise pairs of conveyor chains connected by that said carrier members, and wherein the surface elements of netting have a length extending over at least three successive carrier members as viewed in the conveying direction, said lateral edges of the surface elements extending close to said conveyor chains.
 5. The apparatus according to claim 4, wherein said conveyor chains are sprocket chains, said apparatus further comprising covering means for covering said lateral edges of the surface elements of netting toward the raw material, whereby the covering means prevent the raw material from entering into the space between said screen bottom and said upper run.
 6. The apparatus according to claim 2, comprising further strand type supporting means arranged longitudinally below said netting means surface elements and intermediate said lateral edges of said surface elements.
 7. The apparatus according to claim 1, comprising further cleaning means attached to at least one of said carrier members for cleaning said screen bottom.
 8. The apparatus according to claim 7, wherein said further cleaning means comprise a bar of yieldable material having a surface positioned in contact with the screen bottom whereby cleaning shearing forces are produced when the conveyor means move.
 9. The apparatus according to claim 1, wherein said first mentioned cleaning means for the netting means is equipped with high pressure nozzles.
 10. The apparatus accoRding to claim 1, further comprising drag sheets and means for suspending said drag sheets in said trough in its upper region adjacent to liquid feeding points in the trough, said drag sheets guiding the liquid in predetermined directions and avoiding the formation of foam. 